1. Field of the Invention
This invention relates to aromatic amine scavengers for use in hydrophilic polyurethanes. More particularly, it is directed to scavengers comprising polyols end-capped with aliphatic polyisocyanates.
Recently it was discovered that polyurethane foams contain aromatic amines. Recent evidence has also tended to indicate that certain aromatic amines may represent a health hazard. Although the formation of the aromatic amines is not understood completely, it appears that aromatic isocyanates and possibly their reaction products containing urea and urethane linkages are hydrolyzed to produce free aromatic amines which can be leached from the polyurethane foam. On the other hand, aliphatic isocyanates due to their low reaction rate do not compete successfully with the aromatic isocyanate for functional groups during the polymerization reaction. Therefore, the aliphatic isocyanate scavenger survives polymerization and is thus capable of forming urea addition products with aromatic amines as these are produced. However, aliphatic isocyanates, per se, have the drawback of having a high vapor pressure (boiling ranges of 200-250.degree. C.) so that they lack permanence and may cause unpleasant odors. Additionally, said high vapor pressure drawback also requires that the aliphatic isocyanates be added in relatively large amounts to insure that sufficient is present to react with the aromatic amine after the foaming and drying or postcuring operations.
2. Description of Previously Published Art
Applicants are aware of certain prior art believed to be relevant. Specifically, British Patent No. 1,368,625 describes preparation of polyurethane foams wherein from 1 to 20% by weight of an aliphatic polyisocyanate is employed in combination with conventional polyurethane foam reagents. The function of the aliphatic polyisocyanate appears to be to enhance formation of a dense integral skin during molding of the polyurethane foam. The aliphatic isocyanate is also said to contribute greatly to non-yellowing of the foam.
U.S. Pat. No. 3,790,508 describes light-stable polyurethane foams prepared by reacting a polyol, an aliphatic isocyanate, an aromatic isocyanate, a blowing agent and a catalyst. The aliphatic isocyanate index employed is from about 5 to about 40.
British Patent No. 1,323,955 also describes formulations containing a mixture of aromatic and aliphatic isocyanates, water and a catalyst to cause trimerization of the aromatic isocyanate. The resulting foams are said to possess good physical properties as well as flame-resistance.
In the three aforestated prior art processes the aliphatic diisocyanate reacts to form part of the foam during the foaming reaction.
U.S. Pat. No. 4,211,847 teaches a method of scavenging aromatic amines in polyurethane foams by the use of scavengers selected from the group consisting of cyclohexyl monoisothiocyanates and hindered cycloaliphatic monoisocyanates. However, these scavengers, because of their relatively high vapor pressure, must be employed in relatively large amounts to insure that sufficient scavenger is still present after the foaming and drying to react with the aromatic amine.
3. Objects of the Invention
One object of the instant invention is to produce a class of scavengers for aromatic amines in polyurethanes. Another object of the invention is to produce a class of scavengers for aromatic amines which have low vapor pressures. A further object of the instant invention is to produce a class of scavengers whicn have reduced reactivity towards water and are compatible with the foaming mixture. Other objects will become apparent from a reading hereinafter.